Their Windows/WP/UI projects are violently closed source, almost all cross-platform Rich/UI initiatives have been killed since Sinofsky has taken back the helm. Personally they should do all C#/.NET devs a service and provide better integration/code-reuse with MonoDroid/MonoTouch, but as they don't see it in their best interest they're pushing for platform-lockin. Which is a strange play when you're hopelessly behind the incumbents.
This is starting to be a real problem for .NET devs now (since MS is losing their influence) as they become pawns in Microsoft's platform strategies, whilst we (C# devs) miss out on the most exciting platforms Microsoft doesn't want you to develop for, e.g: iOS/Android, NaCL, Unity3d, RaspPi, etc. We're just lucky Mono exists which runs on all these platforms.